Improve shell portability for plugin installation

Presentation

Using alpine-based images, template fails with errors like /scripts-398824-317360975/step_script: eval: line 743: syntax error: unexpected redirection

Likely because ash/dash, which is the default shell on Alpine, does not support here-string syntax <<< [content / or command].

• get rid of here-string syntax for better portability
• use better yq expression to extract plugin references

Closes

Fixes #56 (closed)

Checklist

• Documented: n/a

• Tested & examplified:

  • (url to a project sample successfully proving the merge request fixes the issue) TBD